Effect of preservation on dinoflagellate and diatom cell volume, and consequences for carbon biomass predictions

Abstract

Plankton biomass estimates are often made using cell size measurements from samples preserved with fixatives such as Lugol's or glutaraldehyde. However, preservation of plankton samples can introduce artifacts to species abundance and cell volume estimates. The goal of this study was to quantify the extent of fixation-induced cell volume change in 18 species of dinoflagellates and 8 species of diatoms in order to provide correction factors to improve biomass estimates. Highly variable and species-specific cell volume changes were found with respect to cell covering, fixative type and strength, time of storage and analysis method (light vs epifluorescence microscopy). Both swelling and shrinking were observed with both fixatives in dinoflagellates and diatoms. Dinoflagellate cell volume changes ranged from over 60% shrinkage to 30% swelling. Cell volume of some diatom species shrank over 30% and swelled almost 30%. These results contradict the common assumption that diatoms are not affected by preservation due to their silica frustule. The observed cell volume changes for both dinoflagellates and diatoms differed from those reported for ciliates and other flagellates. Therefore, application of previously reported correction factors would lead to inaccurate estimates of biovolume and thus carbon biomass. Fixation caused significant changes in biomass predictions of individual dinoflagellate and diatom species. However, biomass estimates for samples containing several species were not significantly different whether based on live or fixed cell volumes.

LISST‐100 measurements of phytoplankton size distribution: evaluation of the effects of cell shape

“…Preservation can result in cell shrinkage or swelling, depending on the species (Booth 1987, Menden Deuer et al 2001. Quantification of the effect of preservation on cell size (volume) of diatoms and dinoflagellates has been reported for fixatives such as Lugol and glutaraldehyde, revealing variations between fixed and nonfixed samples of up to 60% (Menden Deuer et al, 2001); we are not aware of a similar study for formalin. (4) The sample always contains particles other than the cells, which are detected by the LISST-100 but not included in the microscopy analysis.…”

Influence of oceanographic features on spatial and interannual variability of phytoplankton in the Bransfield Strait, Antarctica

“…In the laboratory, 50 to 100 mL sub-samples were analyzed using an inverted microscope, at 200× and 400× magnifications (Utermöhl, 1958). Despite the distinct effects that different fixatives may have on different taxonomic groups (Menden-Deuer et al, 2001), microscopic counting was carefully performed directly after the cruises, in order to minimize variability due to different fixation chemicals on the samples. Phytoplankton composition was determined according to specific literature (Balech, 1988;Dodge, 1982;Hasle and Syvertsen, 1996).…”

Effect of acid Lugol solution as preservative on two representative chitineous and gelatinous zooplankton groups

“…When applying an empirical length to carbon regression for larvaceans (Jaspers et al 2009), carbon biomass is underestimated by 46% when shrinkage effects due to Lugol solution are ignored. We therefore suggest that shrinkage should be carefully addressed and different rates in body size reduction be applied as suggested in the common methodology for ciliates (Putt and Stoecker 1989, Ohman and Snyder 1991, Jerome et al 1993, Stoecker et al 1994) and flagellates (Borsheim and Bratbak 1987, Choi and Stoecker 1989, Menden-Deuer et al 2001.…”

“…All live measurements were conducted in triplicate before direct addition of Lugol to a final concentration of about 2% (Menden-Deuer et al 2001). To evaluate the shrinkage effect over time, the same specimen was measured 2 min (larvaceans only, triplicate measurements), 36 h (single measurement), and 3 months (single measurement) after treatment.…”

“…The effect of Lugol solution on copepod sizes has not been investigated. Most Lugol investigations focused on protozoans and showed a decline in cell volume by 25% to 57%, with a reduction in total length of 3% to 10% (Putt and Stoecker 1989, Montagnes et al 1994, Menden-Deuer et al 2001.…”